1. Field of the Invention
The present invention involves a waterless or driographic lithographic printing plate imageable by a laser emitting infrared or near-infrared radiation at a wavelength between 700 and 1500 nm.
2. Description of Related Art
Waterless printing plates have existed since 1970. Most waterless printing plates involve an ink abhesive layer such as silicone overlying a light absorbing imaging layer. Imaging is typically achieved by exposing the imaging layer to an ultraviolet radiation source then selectively removing the ink abhesive coating. For positive working waterless plates, the imaging layer is a light absorbing layer typically containing a negative working diazo resin as disclosed in U.S. Pat. Nos. 3,511,178; 3,677,178; and 4,775,607; or a light absorbing layer containing a photopolymerizable compound as described in U.S. Pat. Nos. 3,894,873; 5,232,813, and 5,503,074. For negative working waterless plates, imaging is achieved by solubilizing, via ultraviolet radiation, the imaging layer which typically contains diazonaphthoquinones, as described in U.S. Pat. Nos. 4,342,820 and 4,358,522; or imaging a layer that undergoes light-induced acid-catalyzed hydrolysis as described in U.S. Pat. No. 4,842,990. U.S. Pat. No. 3,933,495 describes a dual-tone waterless plate wherein the solubility of the imaging layer is either enhanced or reduced by the developer in the developing step, depending upon developer used.
The majority of the plate manufacturing processes described above require a photographic film, which is expensive and tedious to make. The recent drive for computer-to-plate (CTP) technologies has created the need to develop a new generation of waterless plates, if the advantages of waterless printing are to be maintained for CTP applications.
One method of adapting waterless plate making technology to CTP applications is to generate a contact mask on a photographic waterless plate. The mask could be produced, for example, via a digital device such as an ink jet printer, electrographic printer, or any other apparatus employing a digitally controlled laser. The mask could also be produced by laser ablation, laser ablative transfer, laser induced color change techniques in a photochromic top layer or in a laser-induced solubilized or insolubilized opaque top layer. However, masked printing plates are costly to manufacturing and require more complicated processing such as flood exposing and the removal of the mask.
U.S. Pat. No. 5,339,737 teaches physically transforming an infrared-absorbing layer by laser ablation using high doses of laser energy in order to remove the overlying silicone layer. However, this process is relatively time consuming. In order to circumvent the problem, U.S. Pat. No. 5,353,705 describes adding an ablatable, but non-infrared absorbing, layer, below the infrared absorbing layer. Another approach, taught in U.S. Pat. No. 5,379,698, involves using a metallic or metal oxide thin film as the imaging layer. Yet another approach is taught in U.S. Pat. No. 5,487,338 and involves using an infrared reflective layer situated below the infrared absorbing layer.
All of the above approaches, however, introduce additional cost to the manufacturing of CTP waterless printing plates. In addition, the debris produced during imaging of these printing plates generally requires an additional step and/or complicated devices to clean the plate subsequent to imaging. Despite the improvements made in the manufacture of CTP waterless printing plates, there continues to be a need for a more cost effective and efficient manufacture of high performance CTP waterless printing plates.